Method for forming multi-depth mems package

ABSTRACT

The present disclosure relates to a MEMS package having different trench depths, and a method of fabricating the MEMS package. In some embodiments, a cap substrate is bonded to a device substrate. The cap substrate comprises a first trench, a second trench, and an edge trench recessed from at a front-side surface of the cap substrate. A stopper is disposed within the first trench and raised from a bottom surface of the first trench. The stopper has a top surface lower than the front-side surface of the cap substrate.

REFERENCE TO RELATED APPLICATIONS

This Application is a Divisional of U.S. application Ser. No. 16/705,627, filed on Dec. 6, 2019, which is a Continuation of U.S. application Ser. No. 15/822,538, filed on Nov. 27, 2017 (now U.S. Pat. No. 10,556,790, issued on Feb. 11, 2020). The contents of the above-referenced Patent Applications are hereby incorporated by reference in their entirety.

BACKGROUND

Microelectromechanical systems (MEMS) devices, such as accelerometers, pressure sensors, and microphones, have found widespread use in many modern day electronic devices. For example, MEMS accelerometers are commonly found in automobiles (e.g., in airbag deployment systems), tablet computers, or in smart phones. For some applications, various MEMS devices need to be integrated into one MEMS package; these may include some MEMS sensors requiring different cavity depths.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 illustrates a cross-sectional view of some embodiments of a microelectromechanical systems (MEMS) package.

FIG. 2 illustrates a cross-sectional view of some alternative embodiments of a MEMS package.

FIG. 3 illustrates a cross-sectional view of some alternative embodiments of a MEMS package.

FIGS. 4-10 illustrate a series of cross-sectional views of some embodiments of a MEMS package at various stages of manufacture.

FIG. 11 illustrates a flow diagram of some embodiments of a method for manufacturing a MEMS package.

FIGS. 12-22 illustrate a series of cross-sectional views of some alternative embodiments of a MEMS package at various stages of manufacture.

FIG. 23 illustrates a flow diagram of some alternative embodiments of a method for manufacturing a MEMS package.

DETAILED DESCRIPTION

The present disclosure provides many different embodiments, or examples, for implementing different features of this disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

Moreover, “first”, “second”, “third”, etc. may be used herein for ease of description to distinguish between different elements of a figure or a series of figures. “First”, “second”, “third”, etc. are not intended to be descriptive of the corresponding element. Therefore, “a first dielectric layer” described in connection with a first figure may not necessarily corresponding to a “first dielectric layer” described in connection with another figure.

Multiple MEMS devices may be integrated onto a same integrated chip in recent generations of MEMS ICs. For example, motion sensors are used for motion-activated user interfaces in consumer electronics such as smartphones, tablets, gaming consoles, smart-TVs, and in automotive crash detection systems. To capture a complete range of movements within a three-dimensional space, motion sensors often utilize an accelerometer and a gyroscope in combination. The accelerometer detects linear movement. The gyroscope detects angular movement. To meet consumer demand for low cost, high quality, and small device footprint, the accelerometer and the gyroscope can be integrated together on the same substrate. The accelerometer and the gyroscope utilize different rooms for movement and thus need different cavity depths. One way to fabricate cavities with different depths on the same substrate is to use a series of photolithography and patterning processes. However, after patterning and forming a trench with a first depth in the substrate, the substrate surface becomes non-planar. The subsequent patterning process to form a second trench with a second depth becomes challenging as it is hard to form and pattern a desired photoresist masking layer on the uneven topography of the substrate surface (e.g. insufficient coating or voids may be formed within deep trenches). The case becomes even worse as some additional depth structures such as movement stoppers or subscribe trenches are needed.

The present disclosure is related to a MEMS package having a cap substrate with different trench depths, and a method of fabricating the MEMS package. In some embodiments, a cap substrate is provided having a first device region and a scribe line region defined on the cap substrate. A first trench in the first device region and a scribe trench in the scribe line region are formed at a front side of the cap substrate. Then, a hard mask is formed and patterned over the cap substrate to cover a portion of a bottom surface of the first trench while to expose a remaining portion of the bottom surface of the first trench. Then, with the hard mask in place, an etch is performed to the cap substrate such that the uncovered portion of the bottom surface of the first trench is recessed while the covered portion of the bottom surface of the first trench is non-altered to form a stopper within the first trench. Then, the front side of the cap substrate is bonded to a device substrate, enclosing the first trench over a first MEMS device. Thus, by forming a first trench and then forming and patterning a hard mask within the first trench to prepare for a further etched back (e.g. to form a stopper), different trench depths are formed without applying a masking layer (e.g. a photoresist masking layer) within deep trenches. Comparing to an alternative method to form the stopper by a patterning process performed later in the fabrication process, a required aspect ratio of the patterning openings is reduced. Thereby, an optimized patterning result can be achieved and the fabrication quality is improved.

FIG. 1 shows a cross-sectional view 100 of a MEMS package according to some embodiments. The MEMS package comprises a device substrate 102 and a cap substrate 104 bonded together. In some embodiments, the device substrate 102 may comprise a semiconductor substrate 112 having active elements (e.g., a transistor), an interconnect layer 114 having metallization planes and via interconnects disposed within an inter-metal dielectric (IMD) material, and a MEMS substrate 130 having first MEMS device 106. The cap substrate 104 comprises a device region 110 and a scribe line region 120 defined on the cap substrate 104. The cap substrate 104 encloses a first cavity 116 overlying the first MEMS device 106 within the device region 110 and a scribe trench 117 within the scribe line region 120. In some embodiments, a stopper 119 is raised from a bottom surface 140 s of the first cavity 116 to a position within the first cavity 116 and vertically lower than a front-side surface 126 s of the cap substrate 104. The scribe trench 117 has a bottom surface 142 s located at a position within the cap substrate that is deeper than the bottom surface 140 s of the first cavity 116. In some embodiments, the scribe trench 117 may comprise a peripheral portion having a depth substantially equal to the depth of the first cavity 116, i.e., a surface 144 s of the peripheral portion can be substantially coplanar to the bottom surface 140 s of the first cavity 116. In some embodiments, the cap substrate 104 may further comprise a wafer edge trench 121 disposed within a wafer edge region 122 defined on the boundary region of the cap substrate 104. The wafer edge trench 121 may comprise a bottom surface 146 s that may locate at a substantially same depth with the bottom surface 142 s of the scribe trench 117. The wafer edge trench 121 may further comprise peripheral portion 148 s that may locate at a substantially same depth with a top surface 150 s of the stopper 119. As an example, the first cavity 116, the scribe trench 117, and the wafer edge trench 121 can be formed by a series of fabrication processes shown in FIGS. 4-10, which are described in more detail later.

FIG. 2 shows a cross-sectional view 200 of a MEMS package according to some alternative embodiments. The MEMS package comprises a first MEMS device 106 and a second MEMS device that is respectively enclosed by a first cavity 116 and a second cavity 118 having different depths. A scribe trench 117 has a bottom surface 142 s located at a position within the cap substrate that is deeper than a bottom surface 202 s of the second cavity 118. In some embodiments, the scribe trench 117 may comprise a peripheral portion having a depth substantially equal to the depth of the first cavity 116, i.e., a surface 144 s of the peripheral portion can be substantially coplanar to the bottom surface 202 s of the second cavity 118. A bottom surface 140 s of the first cavity 116 may locate at a position within the cap substrate 104 that is vertically shallower than the 202 s of the second cavity 118. In some embodiments, the cap substrate 104 may further comprise a wafer edge trench 406 having a bottom surface 204 s that may locate at a substantially same depth with a top surface 150 s of the stopper 119. As an example, the first cavity 116, the scribe trench 117, and the wafer edge trench 406 can be formed by a series of fabrication processes shown in FIGS. 12-21, which are described in more detail later. It is understood that some features of the MEMS package described above for FIG. 1 can be incorporated into FIG. 2, and is not repeated here for simplicity reason.

FIG. 3 shows a cross-sectional view of a MEMS package according to some other embodiments. In some embodiments, the MEMS package shown above in FIG. 2 may be subsequent thinned (e.g. from the back-side surface 124 s to a position showed by dash-dotted line 206). The scribe trench 117 may be opened, and a test feature 302 may be exposed for wafer level testing. A singulation process (e.g. dicing) may be subsequently performed.

FIGS. 4-10 show a series of cross-sectional views that collectively depict the formation of a MEMS package according to some embodiments.

As shown in FIG. 4, a cap substrate 104 is prepared. A device region 110, a scribe line region 120 are defined on the cap substrate 104. The scribe line region 120 may be defined surrounding the device region 110. A wafer edge region 122 may be defined at a boundary area of the cap substrate 104. In some embodiments, a bonding layer 132 is disposed on a front-side surface 126 s of the cap substrate 104. The bonding layer 132 and the cap substrate 104 are patterned to form a first trench 402 in the device region 110, a scribe trench 404 in the scribe line region 120, and a wafer edge trench 406 in the wafer edge region 122. The first trench 402, the scribe trench 404, and the wafer edge trench 406 are formed to have a substantially same depth vertically relative to a front-side surface 126 s of the cap substrate 104. In various embodiments, the cap substrate 104 may comprise any type of semiconductor body (e.g., silicon/CMOS bulk, SiGe, SOI, etc.) such as a semiconductor wafer or one or more die on a wafer, as well as any other type of semiconductor and/or epitaxial layers formed thereon and/or otherwise associated therewith. As examples, the bonding layer 132 can be made of metals such as aluminum (Al), germanium (Ge), gold (Au), copper (Cu), Tin (Sn) or alloys.

As shown in FIG. 5, a hard mask 502 is formed on the cap substrate 104. The hard mask 502 may be formed by deposition techniques and may comprise silicon dioxide, silicon nitride, other dielectric materials, or metal depending on applications. The hard mask 502 is formed to fill the first trench 402, the scribe trench 404, and the wafer edge trench 406, and to extend over the bonding layer 132.

As shown in FIG. 6, the hard mask 502 is patterned. As a result of the patterning, a portion of a bottom surface of the first trench 402 is covered (to prepare for a subsequent stopper formation) while a remaining portion of the bottom surface of the first trench 402 is not covered. The hard mask 502 in the scribe trench 404 and a portion of the wafer edge trench 406 are removed by the patterning process. In some embodiments, the hard mask 502 is patterned by an etching process according to a photoresist masking layer 602, which is formed on the hard mask 502 and then patterned by a photolithography process. In various embodiments, the etching process may comprise a wet etch or a dry etch (e.g., a plasma etch with tetrafluoromethane (CF4), sulfur hexafluoride (SF6), nitrogen trifluoride (NF3), etc.). The photoresist masking layer 602 will be substantially removed after the etching processes.

As shown in FIG. 7, a photoresist masking layer 702 is formed on the hard mask 502 and then patterned by a photolithography process to expose at least a portion of the bottom surface of the scribe trench 404 and the wafer edge trench 406. An etch is then performed to the scribe trench 404 to lower a bottom surface of the scribe trench 404. In some embodiments, a central portion 708 s of the bottom surface of the scribe trench 404 is recessed while a peripheral portion 710 s of the bottom surface of the scribe trench 404 is covered by a photoresist masking layer 702. In some embodiments, a portion 704 s of the bottom surface of the wafer edge trench 406 is recessed while a peripheral portion 706 s of the bottom surface of the wafer edge trench 406 is covered by the photoresist masking layer 702. In some alternative embodiments not shown in FIG. 7, the entire or a majority portion of the scribe trench 404 can be recessed by patterning the photoresist masking layer 702 to expose the scribe trench 404.

As shown in FIG. 8, a blanket etch back process is performed to the cap substrate 104 to lower bottom surfaces of the first trench 402, the scribe trench 404, and the wafer edge trench 406 that are not covered by the hard mask 502. The etch back process may be a dry etch using an etchant that is highly selective to the material of the cap substrate 104 than the material of the hard mask 502. As a result, the uncovered portion 802 s of the bottom surface of the first trench 402, the central portion 708 s and the peripheral portion 710 s of the bottom surface of the scribe trench 404, and the portion 704 s of the bottom surface of the wafer edge trench 406 are recessed, while the covered portion 804 s (covered by the hard mask 502) of the bottom surface of the first trench 402 and the portion 704 s of the bottom surface of the wafer edge trench 406 are non-altered. By patterning and lowering the scribe trench 404 first (shown in FIG. 7), and followed by a blanket etch to further lower the scribe trench 404 and the first trench 402 together (shown in FIG. 8), the scribe trench 404 and the first trench 402 are formed having different depths. Comparing to an alternative method to etch the scribe trench 404 and the first trench 402 by separate patterning processes to target depths, a required aspect ratio of the patterning openings is reduced. Also, the work piece has a less height variation at the stage shown in FIG. 7 than a later stage. Thereby, an optimized patterning result can be achieved.

As shown in FIG. 9, the hard mask 502 is removed by a series of etching processes that may comprise dry etching or wet etching. As a result of the blanket etch back process of FIG. 8, the central portion 708 s of the scribe trench 404 and the portion 704 s of the wafer edge trench 406 may locate at a substantially same depth within the cap substrate 104. The peripheral portion 706 s of the wafer edge trench 406 and the covered portion 804 s of the first trench 402 may locate at a substantially same depth within the cap substrate 104.

As shown in FIG. 10, the cap substrate 104 is flipped over and bonded to a device substrate 102. For example, the bonding layer 132 of the cap substrate 104 are bonded by a eutectic bonding process to the corresponding bonding elements 134 of the device substrate 102, such that the device substrate 102 and the cap substrate 104 are physically and electrically connected. The device substrate 102 may be prepared by providing a semiconductor substrate 112, which has been prepared through one or more fabrication processes. For example, the semiconductor substrate 112 includes one or more active elements. A series of metallization planes and via interconnects are disposed within an IMD layer 114 formed over an upper surface of the semiconductor substrate 112. A MEMS substrate 130 comprising the first and second MEMS devices 106, 108 is bonded to the semiconductor substrate 112 through IMD layer 114 to form a device substrate 102. For example, the MEMS substrate 130 can be bonded to the IMD layer 114 by a fusion bonding process. In some embodiments, a fusion bonding is achieved between the IMD layer 114 comprising SiO₂ and the MEMS substrate 130 comprising Si. In some embodiments, the MEMS substrate 130 and/or the semiconductor substrate 112 is thinned down to reduce the thickness thereof after fusion bonding.

FIG. 11 shows a flow diagram of a method 1100 for manufacturing a MEMS package according to some embodiments. The MEMS package comprises two MEMS devices with different cavity depths. Examples of the MEMS package are shown in FIG. 1.

While disclosed methods (e.g., methods 1100) are illustrated and described below as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events is not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases. Although the method 1100 is described in relation to FIGS. 4-10, it will be appreciated that the method 1100 is not limited to the structures disclosed in FIGS. 4-10, but instead may stand alone independent of the structures disclosed in FIGS. 4-10.

At action 1102, a first trench is formed in a device region and a scribe trench is formed in scribe line region of a cap substrate. FIG. 4 shows a cross-sectional view corresponding to action 1102 according to some embodiments.

At action 1104, a hard mask is formed and patterned to cover a portion of the first trench. FIGS. 5-6 show cross-sectional views corresponding to action 1104 according to some embodiments.

At action 1106, an etch is performed to lower a bottom surface of the scribe trench. FIG. 7 shows a cross-sectional view corresponding to action 1106 according to some embodiments.

At action 1108, with the hard mask in place, an etch is performed to the cap substrate to form a stopper within the first trench. FIGS. 8-9 show cross-sectional views corresponding to action 1108 according to some embodiments.

At action 1110, the cap substrate is bonded to a device substrate to form the MEMS package. FIG. 10 shows a cross-sectional view corresponding to action 1110 according to some embodiments.

FIGS. 12-22 show a series of cross-sectional views that collectively depict the formation of a MEMS package according to some embodiments. The MEMS package comprises at least two MEMS devices with different cavity depths.

As shown in FIG. 12, a cap substrate 104 is prepared. A first device region 110 a and a second device region 110 b are defined on the cap substrate 104. A scribe line region 120 may be defined surrounding the first device region 110 a and the second device region 110 b. A wafer edge region 122 may be defined at a boundary area of the cap substrate 104. In some embodiments, a bonding layer 132 is disposed on a front-side surface 126 s of the cap substrate 104. The bonding layer 132 and the cap substrate 104 are patterned to form a first trench 402 a in the first device region 110 a, a second trench 402 b in the second device region 110 b, a scribe trench 404 in the scribe line region 120, and a wafer edge trench 406 in the wafer edge region 122. The first trench 402 a, the second trench 402 b, the scribe trench 404, and the wafer edge trench 406 are formed to have a substantially same depth vertically relative to a front-side surface 126 s of the cap substrate 104. In various embodiments, the cap substrate 104 may comprise any type of semiconductor body (e.g., silicon/CMOS bulk, SiGe, SOI, etc.) such as a semiconductor wafer or one or more die on a wafer, as well as any other type of semiconductor and/or epitaxial layers formed thereon and/or otherwise associated therewith. As examples, the bonding layer 132 can be made of metals such as aluminum (Al), germanium (Ge), gold (Au), copper (Cu), Tin (Sn) or alloys.

As shown in FIG. 13, a hard mask 502 is formed on the cap substrate 104. The hard mask 502 may be formed by deposition techniques and may comprise silicon dioxide, silicon nitride, other dielectric materials, or metal depending on applications. The hard mask 502 is formed to fill the first trench 402 a, the second trench 402 b, the scribe trench 404, and the wafer edge trench 406, and to extend over the bonding layer 132.

As shown in FIG. 14, a first patterning process is performed to the hard mask 502. As a result of the patterning, the hard mask 502 is recessed at the second trench 402 b and a portion of the first trench 402 a while a remainder of the hard mask 502 is covered by a first masking layer 1402 (e.g. a photoresist masking layer) and not altered. The patterning process produces and prepares a depth difference of the hard mask 502 for the portions within the first trench 402 a. Thereby, a stopper can be subsequently formed self-aligned without a patterning process (referring to the stopper 119 formed in FIGS. 18-19 below). Comparing to an alternative method to form the stopper by a patterning process performed later in the fabrication process, a required aspect ratio of the patterning openings is reduced. The work piece has a less height variation at the stage shown in FIG. 14 than a later stage. Thereby, an optimized patterning result can be achieved.

As shown in FIG. 15, a second patterning process is performed to the hard mask 502 with a second masking layer 1502 (e.g. a photoresist masking layer) in place. As a result of the patterning, the hard mask 502 within the second trench 402 b and the scribe trench 404 are removed while a remainder of the hard mask 502 is not altered. As an alternative embodiment not shown in FIG. 14. The first masking layer 1402 can cover the second trench 402 b, such that the hard mask 502 within the second trench 402 b is not recessed in FIG. 14, and completely removed in FIG. 15. The patterning process exposes the second trench 402 b and the scribe trench 404 while has the first trench 402 a protected by the hard mask 502. Thereby, a depth difference can be subsequently formed by a series of etching processes. Comparing to an alternative method to form the first trench 402 a and the second trench 402 b with different depths by a patterning process performed later in the fabrication process, a required aspect ratio of the patterning openings is reduced. The work piece has a less height variation at the stage shown in FIG. 15 than a later stage. Thereby, an optimized patterning result can be achieved.

As shown in FIG. 16, a third masking pattern 1602 (e.g. a photoresist masking layer) is formed and patterned to expose a central portion 708 s of the bottom surface of the scribe trench 404 while to cover a peripheral portion 710 s of the bottom surface of the scribe trench 404. An etch is then performed to the scribe trench 404 to lower the central portion 708 s of a bottom surface of the scribe trench 404 while not alter the peripheral portion 710 s of the bottom surface of the scribe trench 404. Similarly, by lowering the bottom surface of the scribe trench 404 first followed by a blanket etch to further lower the scribe trench 404 and the first trench 402 a together, the scribe trench 404 and the first trench 402 a are formed having different depths. Comparing to an alternative method to etch the scribe trench 404 and the first trench 402 a by separate patterning processes to target depths, a required aspect ratio of the patterning openings is reduced. Also, the work piece has a less height variation at the stage shown in FIG. 16 than a later stage. Thereby, an optimized patterning result can be achieved. The masking layers 1402, 1502, 1602 are formed on the hard mask 502 and then patterned by photolithography process(es). In some embodiments, the wafer edge trench 406 can be alternatively patterned similarly to what is shown and described in FIGS. 7-8.

As shown in FIG. 17, the third masking layer 1602 (shown in FIG. 16) is removed, and a first blanket etch is performed to the cap substrate 104. The third masking pattern 1602 may be removed by a wet etching process followed by a wafer cleaning process. The first blanket etch may comprise an anisotropic (e.g. vertical) dry etch. As an etching result, lateral surfaces of the cap substrate 104 not covered by the hard mask 502 is recessed, which may include a bottom surface 1702 s of the second trench 402 b, the central portion 708 s and the peripheral portion 710 s of the bottom surface of the scribe trench 404. The etch back process may be a dry etch using an etchant that is highly selective to the material of the cap substrate 104 than the material of the hard mask 502.

As shown in FIG. 18, a second blanket etch is performed to the hard mask 502, such that the hard mask 502 is vertically lowered, and a portion 802 s of the bottom surface of the first trench 402 a is exposed. The second blanket etch may comprise a dry etch using an etchant that is highly selective to the material of the hard mask 502 than the material of the cap substrate 104.

As shown in FIG. 19, a third blanket etch is performed to the cap substrate 104. The exposed portion 802 s of the bottom surface of the first trench 402 a is recessed together with the bottom surface 1702 s of the second trench 402 b, the central portion 708 s and the peripheral portion 710 s of the bottom surface of the scribe trench 404. A stopper 119 is formed within the first trench 402 a with the exposed portion 802 s of the bottom surface recessed from the covered portion 804 s of the bottom surface of the first trench 402 a. The second blanket dry etch may comprise a dry etch using an etchant that is highly selective to the material of the hard mask 502 than the material of the cap substrate 104.

As shown in FIG. 20, a series of etching processes is performed to remove the hard mask 502 (shown in FIG. 19). The etching processes may comprise dry etching or wet etching and may selective to the hard mask 502.

As shown in FIG. 21, the cap substrate 104 is flipped over and bonded to a device substrate 102. For example, the bonding layer 132 of the cap substrate 104 are bonded by a eutectic bonding process to the corresponding bonding elements 134 of the device substrate 102, such that the device substrate 102 and the cap substrate 104 are physically and electrically connected. Upon bonding, the first trench 402 a (shown in FIG. 20) becomes part of the first cavity 116 enclosing a first MEMS device 106; and the second trench 402 b becomes part of the second cavity 118 enclosing a second MEMS device 108. The device substrate 102 may be provided including a semiconductor substrate 112 with one or more active elements. A series of metallization planes and via interconnects are disposed within an IMD layer 114 formed over an upper surface of the semiconductor substrate 112. A MEMS substrate 130 comprising the first and second MEMS devices 106, 108 is bonded to the semiconductor substrate 112 through IMD layer 114 to form the device substrate 102. For example, the MEMS substrate 130 can be bonded to the IMD layer 114 by a fusion bonding process. In some embodiments, a fusion bonding is achieved between the IMD layer 114 comprising SiO₂ and the MEMS substrate 130 comprising Si. In some embodiments, the MEMS substrate 130 and/or the semiconductor substrate 112 is thinned down to reduce the thickness thereof after fusion bonding. In some embodiments, the eutectic bond includes a semiconductor-to-metal bonding between a semiconductor material and a metal material. In some embodiments, the semiconductor material includes at least one of Ge, Si, SiGe or another semiconductor material. In some embodiments, the metal material includes at least one of Al, Cu, Ti, Ta, Au, Ni, Sn, or another metal. Another example of eutectic bonding is a metal-to-metal bonding between two metal materials each including at least one of Al, Cu, Ti, Ta, Au, Ni, Sn, or another metal. The materials to be bonded are pressed against each other in an annealing process to form a eutectic phase of the materials. For example, a eutectic bonding between Ge and Al is formed at an annealing temperature in a range from 400° C. to 450° C.

As shown in FIG. 22, in some embodiments, the cap substrate 104 is then thinned down to remove a partial thickness after being bonded to the device substrate 102. The scribe trench 404 may be exposed. The exposed scribe trench 404 may provide test points for the bonded wafer or other functions before dicing into singulated pieces.

FIG. 23 shows a flow diagram of a method 2300 for manufacturing a MEMS package according to some embodiments. The MEMS package comprises two MEMS devices with different cavity depths. Examples of the MEMS package are shown in FIG. 2.

While disclosed methods (e.g., methods 2300) are illustrated and described below as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events is not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases. Although the method 2300 is described in relation to FIGS. 12-22, it will be appreciated that the method 2300 is not limited to the structures disclosed in FIGS. 12-22, but instead may stand alone independent of the structures disclosed in FIGS. 12-22.

At action 2302, a first trench and a second trench are respectively formed in a first device region and a second device region, and a scribe trench is formed in scribe line region of a cap substrate. FIG. 12 shows a cross-sectional view corresponding to action 2302 according to some embodiments.

At action 2304, a hard mask is formed and patterned such that a bottom surface of the hard mask is recessed at the second trench and a portion of the first trench while a remainder of the hard mask is covered by a first masking layer. FIGS. 13-14 show cross-sectional views corresponding to action 2304 according to some embodiments.

At action 2306, a second patterning process is performed to the hard mask to be removed from the second trench and the scribe trench. FIG. 15 shows a cross-sectional view corresponding to action 2306 according to some embodiments.

At action 2308, an etch is performed to lower a bottom surface of the scribe trench. FIG. 16 shows a cross-sectional view corresponding to action 2308 according to some embodiments.

At action 2310, with the hard mask in place, a blanket etch is performed to the cap substrate to lower bottom surface of the second trench and the scribe trench. The first trench is covered and protected by the hard mask. FIG. 17 shows a cross-sectional view corresponding to action 2310 according to some embodiments.

At action 2312, perform a series of etching processes to the hard mask and the cap substrate to form a stopper within the first trench. The hard mask is then removed. FIGS. 18-20 show cross-sectional views corresponding to action 2312 according to some embodiments.

At action 2314, the cap substrate is bonded to a device substrate to enclose a first MEMS device and a second MEMS device with different cavity depths and form the MEMS package. FIG. 21 shows a cross-sectional view corresponding to action 2314 according to some embodiments.

At action 2316, the back-side of cap substrate is thinned to expose the scribe trench. The exposed scribe trench may provide test points for the bonded wafer or other functions before dicing into singulated pieces. FIG. 22 shows a cross-sectional view corresponding to action 2316 according to some embodiments.

Thus, as can be appreciated from above, the present disclosure relates to a MEMS package and associated methods. In some embodiments, a first trench in a first device region and a scribe trench in a scribe line region are formed at a front side of a cap substrate. Then, a hard mask is formed and patterned over the cap substrate. Then, with the hard mask in place, an etch is performed to the cap substrate such that an uncovered portion of a bottom surface of the first trench is recessed while a covered portion of the bottom surface of the first trench is non-altered to form a stopper within the first trench. Then, the front side of the cap substrate is bonded to a device substrate, enclosing the first trench over a first MEMS device. Thus, by forming a first trench and then forming and patterning a hard mask within the first trench to prepare for a further etched back (e.g. to form a stopper), different trench depths are formed without applying a photoresist masking layer within deep trenches. Thereby, fabrication quality is improved.

In some embodiments, the present disclosure relates to a microelectromechanical systems (MEMS) package. A cap substrate is bonded to a device substrate. The cap substrate comprises a first trench, a second trench, and an edge trench recessed from at a front-side surface of the cap substrate. A stopper is disposed within the first trench and raised from a bottom surface of the first trench. The stopper has a top surface lower than the front-side surface of the cap substrate.

In other embodiments, the present disclosure relates to a a microelectromechanical systems (MEMS) package. A device substrate comprises a first MEMS device and a second MEMS device. A cap substrate is bonded to the device substrate. The cap substrate comprises a first trench overlying the first MEMS device, a second trench overlying the second MEMS device, and a scribe trench disposed in a scribe line region and recessed from a front-side surface of the cap substrate. A stopper is disposed within the first trench and raised from a bottom surface of the first trench to a position vertically lower than the front-side surface of the cap substrate.

In yet other embodiments, the present disclosure relates to a microelectromechanical systems (MEMS) package. A device substrate comprises a first MEMS device and a second MEMS device. A cap substrate is bonded to the device substrate. The cap substrate encloses a first cavity overlying the first MEMS device and a second cavity overlying the second MEMS device. The first cavity has a first depth with respect to a front-side surface of the cap substrate smaller than a second depth of the second cavity with respect to the front-side surface of the cap substrate. A stopper is raised from a bottom surface of the first cavity to a position within the first cavity and vertically lower than the front-side surface of the cap substrate.

The foregoing outlines feature of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A microelectromechanical systems (MEMS) package, comprising: a cap substrate bonded to a device substrate, the cap substrate comprising a first trench, a second trench, and an edge trench recessed from at a front-side surface of the cap substrate; and a stopper disposed within the first trench and raised from a bottom surface of the first trench; wherein the stopper has a top surface lower than the front-side surface of the cap substrate.
 2. The MEMS package of claim 1, wherein the stopper has a stopper height vertically between the top surface and the front-side surface of the cap substrate that is equal to a first vertical distance between a first lateral surface of the edge trench and the front-side surface of the cap substrate.
 3. The MEMS package of claim 1, wherein the first trench has a first depth with respect to a front-side surface of the cap substrate smaller than a second depth of the second trench with respect to the front-side surface of the cap substrate.
 4. The MEMS package of claim 3, wherein the first depth is equal to a second vertical distance between a second lateral surface of the edge trench and the front-side surface of the cap substrate.
 5. The MEMS package of claim 4, wherein the second depth is equal to a third vertical distance between a third lateral surface of the edge trench and the front-side surface of the cap substrate.
 6. The MEMS package of claim 3, wherein the second trench has an intermediate lateral surface between a bottom surface of the second trench and the front-side surface of the cap substrate.
 7. The MEMS package of claim 6, wherein an intermediate depth of the second trench vertically between the intermediate lateral surface and the front-side surface of the cap substrate is equal to the first depth.
 8. A microelectromechanical systems (MEMS) package, comprising: a device substrate comprising a first MEMS device and a second MEMS device; and a cap substrate bonded to the device substrate, the cap substrate comprising a first trench overlying the first MEMS device, a second trench overlying the second MEMS device, and a scribe trench disposed in a scribe line region and recessed from a front-side surface of the cap substrate; wherein a stopper is disposed within the first trench and raised from a bottom surface of the first trench to a position vertically lower than the front-side surface of the cap substrate.
 9. The MEMS package of claim 8, wherein the first trench has a first depth with respect to a front-side surface of the cap substrate smaller than a second depth of the second trench with respect to the front-side surface of the cap substrate.
 10. The MEMS package of claim 9, wherein the scribe trench has an intermediate lateral surface between a bottom surface of the scribe trench and the front-side surface of the cap substrate.
 11. The MEMS package of claim 10, wherein the intermediate lateral surface is located in a vertical depth same as the second depth.
 12. The MEMS package of claim 11, further comprising an edge trench in a boundary region of the cap substrate having a depth equal to that of the scribe trench.
 13. The MEMS package of claim 12, wherein the edge trench has a first lateral surface having a first vertical distance with respect to the front-side surface of the cap substrate that is equal to a height of the stopper with respect to the front-side surface of the cap substrate.
 14. The MEMS package of claim 13, wherein the edge trench has a second lateral surface having a second vertical distance with respect to the front-side surface of the cap substrate that is equal to the first depth.
 15. The MEMS package of claim 14, wherein the edge trench has a third lateral surface having a third vertical distance with respect to the front-side surface of the cap substrate that is equal to a scribe depth of the scribe trench.
 16. The MEMS package of claim 8, wherein the device substrate and the cap substrate are bonded by a pair of bonding elements through a eutectic bonding.
 17. The MEMS package of claim 16, wherein the pair of bonding elements is disposed between the first MEMS device and the second MEMS device.
 18. A microelectromechanical systems (MEMS) package, comprising: a device substrate comprising a first MEMS device and a second MEMS device; and a cap substrate bonded to the device substrate, the cap substrate enclosing a first cavity overlying the first MEMS device and a second cavity overlying the second MEMS device; wherein the first cavity has a first depth with respect to a front-side surface of the cap substrate smaller than a second depth of the second cavity with respect to the front-side surface of the cap substrate; and wherein a stopper is raised from a bottom surface of the first cavity to a position within the first cavity and vertically lower than the front-side surface of the cap substrate.
 19. The MEMS package of claim 18, further comprising a scribe trench disposed within the cap substrate, wherein the scribe trench comprises a central portion having a third depth greater than the second depth of the second cavity and a peripheral portion with an intermediate depth smaller than the third depth.
 20. The MEMS package of claim 19, wherein the intermediate depth is equal to the second depth. 